Directional control valve

ABSTRACT

A four-way spool valve assembly embodying a regenerative circuit for controlling the actuation of a double acting fluid motor for a bulldozer blade or the like characterized in that the spool has therewithin a relief valve and a check valve respectively operative to build up back pressure in the return line from the rod end of the motor during the blade lowering operation and to permit return flow under such back pressure into the inlet port to prevent cavitation of the head end of the motor, and further characterized in that the spool has a float position in which a bypass passage in the assembly is open for flow of fluid from the inlet passage to the return passage and in which both motor ports have unrestricted communication with the return passage.

[ Dec.4,1973

[ DIRECTIONAL CONTROL VALVE [75] Inventor: Herbert H. Schmiel, Minneapolis,

Minn.

[73] Assignee: Parker-Hannifin Corporation,

Cleveland, Ohio [22] Filed: Feb. 17, 1972 a [21] Appl. No.: 227,212

- [52] U.S. CL... 137/596.12, 137/624.27, 137/625.68

[51] Int. Cl. F15b 21/00, F16k 17/26, F16k 17/32 [58] Field 01 Search l3,7/596.12, 596.13, 137/5961, 596.2, 625.68, 596; 91/414, 411;

Primary Examinerl-lenry T. Klinksiek Assistant Examiner-Robert J. Miller Attorney-Walter Maky [57] ABSTRACT A four-way spool valve assembly embodying a regenerative circuit for controlling the actuation of a double acting fluid motor for a bulldozer blade or the like characterized in that the spool has therewithin a relief valve and a check valve respectively operative to build up back pressure in the return line from the rod end of the motor during the blade lowering operation and to permit return flow under such back pressure into the inlet port to prevent cavitation of the head end of the motor, and further characterized in that the spool has a float position in which a bypass passage in the assembly is open for flow of fluid from the inlet passage to the return passage and in which both motor ports have unrestricted communication with the return passage.

6 Claims, 1 Drawing Figure RAISE TANK WENIEDBEC 41975 TANK -EuTRAL---- RAISE DIRECTIONAL CONTROL VALVE BACRGROND OF THE INVENTION It is known to provide regenerative circuits as abovementioned in connection with front end loaders, for example to prevent fluid motor cavitation as during the load (boom and bucket) lowering operation thereof when the load on the motor tends to run ahead of the 1 pump. See, for example, the application of Rice Ser.

No. 1,715, filed Jan. 9, 1970, now US. Pat. No. 3,642,027 granted Feb. 15, 1972, wherein the spool is hollow and has thereina relief valve and a check valve respectively operative to build up back pressure in the return line from the motor during the load lowering operation and to permit return flow under such back pressure into the inlet port to prevent cavitation of the fluid motor.

It is'also known to provide a four-way spool type valve assembly in which the spool has a float position to permit movement of the piston of a fluid motor in a direction such that oil coming out of the head end of the cylinder is conducted to the rod end of the cylinder via a passage in the spool with excess flow passing through a spring loaded valve or an orifice leading to the low pressure side of the valve assembly. For examples of this type of four-way float spool, reference may be had to the following US. Pat. Nos.: Schmiel 3,000,397; Stacey 3,106,065; Markovich 3,120,858; Stacey 3,132,688; Schmiel et al. 3,160,174; Stacey 3,195,559; 3,251,277; 3,262,467; 3,299,903.

In the case of equipment such as a front end loader the downward float of the boom and bucket displaces oil from the head end of the cylinder to the rod end with excess flow being conducted to the low pressure side of the valve assembly. However, in the case of a bulldozer or the like, the bulldozer blade may be employed for back dragging while the valve assembly is in the float position and hence oil is discharged from the rod end of the cylinder to the head end. Accordingly, such orifice communication of the motor ports with the 1 low pressure side of the valve assembly as described in the aforementioned patents cannot be used because oil wouldhave tobe drawn into the head end of the cylinder through suchrestricted orifice thereby causing cavitation in the head endof the motor. In such bulldozer application it is of course necessary when the blade is in operating position to press it firmly against the ground and hence oil under pressure is admitted into the head end of the cylinder for maximum ground engaging force, whereas-in a front end loader or the like, oil is admittedinto the head end of the cylinder to raise the boom and bucket.

SUMMARY OF THE INVENTION ln view of the foregoing, it is a primary object of the present invention to provide a four-way spool type valve assembly for bulldozer and like applications which has a regenerative circuit built into the hollow spool thereof to obtain fast power lowering of the bulldozer blade to ground-engaging position and which, in addition, has a float position permitting free flow of oil between the low pressure side of the assembly and the motor ports during the back dragging operation of the bulldozer.

Other objectsand advantages of the present invention will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTION The directional control valve assembly 1 herein shown comprises a housing 2 having a pressureinlet port 3 adapted for connection with a pump 4, a return port 5 adapted for connection with a tank 6, and a pair of motor ports 7;7 adapted for connection with a double acting fluid motor 8.

The housing 2 is of conventional form having a bore 9 therethrough for a spool 10, said bore 9 being intersected axially therealong starting from the middle by a bypass passage portion 11 which leads to the return port 5, said bypass portion 11 being straddled by bypass portion 12;l2 leading to the inlet port3, a pair of pressure feed passages 14;14 which straddle the aforesaid bypass portions 12;]2 and which communicate with the inlet port 3 via load check valves l5;15,a pair of motor passages 16;16 which straddle thepressure feed passages l4;14 and which leadto the respective motor ports 7;7, and a pair of return passages 17;]7 which straddle the motor passages l6;l6 and which lead to the return port 5. Between the inlet port 3 and one return passage 17 is the main relief valve 1 3.

When the spool 10 is in NEUTRAU'position in which it is held by the spring centering mechanism 18,

fluid delivered by the pump 4 to the inlet port 3 freely circulates through the by-pass passages 12;12 and 11 back to the tank 6 through the return port 5, and the motor passages 16;l6 are blocked from communicating with the return passages l7;17 and with the pressure ,feed passages 14;]4 by the respective spool lands 19;]9

and 20;20, wherebythe bulldozer blade 21 and boom 22 will remain in whatever position they happen to be when the spool 10 is allowed to be shifted by the spring centering mechanism 18 to NEUTRAL" position.

In one end of the spool 10 is a relief valve member 23 which is actuated to seatedposition by the spring 24 and which is operative to maintain a predetermined back pressure in the regeneration path hereinafter to be described when the spool 10 is in LOWER position, said relief valve member 23, when actuated by pressure exceeding the predetermined back pressure, opening a first passage constituted by the openings 25, the bore 26, and the holes 27 which register with the holes 28 in the sleeve 29 to relieve excess pressure to the return passage. 17. The sleeve 29 aforesaid preferably has a slide fit with the spool 10, and a loose fit in the counterbore 30 in the housing 2, and a gasket 31 is provided between the bottom of the counterbore30 and the lower end of the sleeve 29 to form a sealed joint thereat when the sleeve 29 is clamped in place by the spring centering mechanism .18.

In the other end of the spool 10 is a check valve member 32 which is urged to seated position by the spring 34 and which is operative to open a second passage in the regeneration path which is constituted by the openings 25, the bore 35, and theopenings. 36 for flow of fluid into the lower bypass passage portion 12 to supplement the fluid delivered by the pump 4 thus to prevent cavitation when the spool 10 is in its power LOWER position. This provides for fast lowering of the blade 21 to ground engaging position.

When it is desired to lower the boom 22 with the blade 21 firmly engaging the ground as aforesaid, the spool is shifted upwardly from NEUTRAL position to LOWER position, whereat the spool lands 37 and 20 close communication between the bypass portions 12 and 11 for flow of fluid under pressure delivered by the pump through the lower check valve to the lower pressure feed passage 14 and thence to the lower motor passage 16 via the spool groove 38 whereby fluid under pressure is conducted into the head end of the motor 8 to move the boom 22 and blade 21 downwardly. Oil displaced from the rod end of the motor 8 flows into the upper motor passage 16 and because of the closed position of the relief valve member 23 pressure builds up in the upper motor passage 16 and effects unseating of the check valve member 32, whereby the fluid returning to the valve assembly 1 from the rod end of the motor 8 is conducted into the inlet port 3 to the supplement the pump 4 output, thus to achieve rapid lowering of the boom under power control and without permitting cavitation of the head end of the motor 8.

As the blade 21 contacts the ground, pressure starts to build up in the inlet port 3 sufficient to close the check valve member 32 and the increased pressure in the upper motor passage 16 acting on the area of the relief valve member 23 moves the same to open position and when opened the pressure drop across the annular orifice 39 acting on the larger diameter of the relief valve member 23 opens the relief valve member 23 further and maintains it open for prompt reduction of pressure in the return circuit to a value less than initially required to unseat the relief valve member 23. Thus, the increased pressure acts on the head end of the motor 8 to firmly press the blade 21 into the ground.

When it is desired to raise the boom 22 and blade 21, the spool 10 is shifted downwardly from NEUTRAL" position to RAlSE" position whereat the spool lands 37 and block communication between the bypass portions 12 and 11 with fluid under pressure in the inlet port 3 being conducted through the upper check valve 15 into the upper pressure feed passage 14 and thence into the upper motor passage 16 (via the spool groove 40) and into the rod end of the motor 8. Fluid displaced from the head end of the motor 8 is conducted to the lower motor passage 16 and to the lower return passage (via the spool groove 38). In such RAISE position the upper spool land 19 blocks the sleeve openings 28 to prevent loss of pressure fluid from the upper pressurized motor passage 16. When the force on the spool 10 is released, the spring centering mechanism 18 will return the spool 10 from the RAISE" position back to NEUTRAL position.

When the spool 10 is in FLOAT" position as shown in FIG. 1, the boom 22 and blade 21 may float up or down, the lower motor passage 16 being communicated with the lower return passage 17 by way of the spool groove 41, and the upper motor passage 16 being communicated with the upper return passage 17 by way of the spool groove 40 and the sleeve openings 28. in FLOAT position the bypass passage 12-11 is open as shown.

I, therefore, particularly point out and distinctly claim as my invention:

1. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; a valve spool movable in said housing to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having first and second grooves respectively communicating one motor port selectively with said inlet port and said return port and the other motor port with said inlet port when said one motor port is communicated with said return port via said first groove; said valve spool, in addition to said grooves, having first and second passages therein respectively communicating said other motor port with said return port and with said inlet port when said one motor port is communicated with said inlet port; a relief valve in said first passage to build up back pressure in returning fluid in said other motor port; and a check valve in said second passage permitting returning fluid flow into said inlet port in the event of decrease of fluid pressure in said inlet port to a value less than the back pressure in said other motor port when said spool is in a position communicating said inlet port with said one motor port; the improvement which comprises a valve spool having a float position whereat both motor ports are communicated with said return port via said second groove and via a third groove in said spool adjacent to said first groove.

2. The valve assembly of claim 1 wherein said first and second passages, upstream of said relief valve and check valve, are communicated with said other motor port via said second groove when said spool is in a position communicating said inlet port with said one motor port.

3. The valve assembly of claim 2 wherein said first passage, downstream of said relief valve, terminates in an opening through a spool land adjacent to said second groove; and wherein said housing has a sleeve therein having an opening therethrough communicating with said return port and registering with said land opening when said spool is in a position communicating said inlet port with said one motor port.

4. The valve assembly of claim 3 wherein said spool, when in said float position, communicates said other motor port with said return port via said second groove and said sleeve opening, said spool land covering said sleeve opening when said spool is in a position communicating said inlet port with said other motor port via said second groove.

5. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; and a valve spool movable in said housing to two operating positions to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having first and second grooves selectively communicating said motor ports with said inlet and return ports; the improvement which comprises a valve spool having a third groove adjacent to said first groove operative in conjunction with said second groove to communicate each motor port with said return port upon movement of said valve spool to a third operating position whereby the movable component of the fluid motor may float in opposite directions.

6. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; and a valve spool movable in said housing to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having two operating positions whereat first and second grooves therein selectively communicate said motor ports with said inlet and return ports; the improvement which comprises a valve spool having a third operating position whereat one motor port is freely communicated with said return port via said second groove and the other motor port is freely communicated with said 

1. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; a valve spool movable in said housing to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having first and second grooves respectively communicating one motor port selectively with said inlet port and said return port and the other motor port with said inlet port when said one motor port is communicated wIth said return port via said first groove; said valve spool, in addition to said grooves, having first and second passages therein respectively communicating said other motor port with said return port and with said inlet port when said one motor port is communicated with said inlet port; a relief valve in said first passage to build up back pressure in returning fluid in said other motor port; and a check valve in said second passage permitting returning fluid flow into said inlet port in the event of decrease of fluid pressure in said inlet port to a value less than the back pressure in said other motor port when said spool is in a position communicating said inlet port with said one motor port; the improvement which comprises a valve spool having a float position whereat both motor ports are communicated with said return port via said second groove and via a third groove in said spool adjacent to said first groove.
 2. The valve assembly of claim 1 wherein said first and second passages, upstream of said relief valve and check valve, are communicated with said other motor port via said second groove when said spool is in a position communicating said inlet port with said one motor port.
 3. The valve assembly of claim 2 wherein said first passage, downstream of said relief valve, terminates in an opening through a spool land adjacent to said second groove; and wherein said housing has a sleeve therein having an opening therethrough communicating with said return port and registering with said land opening when said spool is in a position communicating said inlet port with said one motor port.
 4. The valve assembly of claim 3 wherein said spool, when in said float position, communicates said other motor port with said return port via said second groove and said sleeve opening, said spool land covering said sleeve opening when said spool is in a position communicating said inlet port with said other motor port via said second groove.
 5. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; and a valve spool movable in said housing to two operating positions to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having first and second grooves selectively communicating said motor ports with said inlet and return ports; the improvement which comprises a valve spool having a third groove adjacent to said first groove operative in conjunction with said second groove to communicate each motor port with said return port upon movement of said valve spool to a third operating position whereby the movable component of the fluid motor may float in opposite directions.
 6. In a spool valve assembly having a housing including a pressure inlet port, a return port, and a pair of motor ports; and a valve spool movable in said housing to control actuation of a double acting fluid motor adapted to be connected to said motor ports and having two operating positions whereat first and second grooves therein selectively communicate said motor ports with said inlet and return ports; the improvement which comprises a valve spool having a third operating position whereat one motor port is freely communicated with said return port via said second groove and the other motor port is freely communicated with said return port via a third groove in said spool which is adjacent to said first groove thus to permit free floating of the movable component of the fluid motor in opposite directions. 